An optical fiber is produced by drawing a glass preform having a substantially columnar form into a fiber by heating and softening an end thereof. The glass preform for optical fibers is manufactured by manufacturing methods, such as OVD method or MCVD method. Japanese translation of PCT international application No. 2002-543026 (Patent Literature 1) discloses a method for manufacturing a glass preform by OVD method.
The glass-preform manufacturing method disclosed in Patent Literature 1 is intended to produce glass preforms for optical fibers with low water content. According to this manufacturing method, a glass soot body is produced by depositing glass particles on the circumferences of a starting mandrel and a tubular handle in which the starting mandrel is inserted, and then a glass soot body having a central hole along the axial direction is produced by pulling out the starting mandrel from the glass soot body. Subsequently, the glass soot body is heated to be dry and consolidated, and then the central hole thereof is collapsed. Thus, a transparent glass preform is produced.